Electric furnace



Re. 212,2 74 y ELECTRIC FURNACE Original Filed oct. 1o, i938 muy mm1 i INVENTORI @mu/Q. Gm

BY KM www xGWW/z ATTORNEYS' Reieeueel rel. 23, 1943 ynrlltc'rrucritntliuicll Daniel Gardner, New n: N. Y., by k' Thermal mesne assignments, to Gardner Corporation, a corporation of Delaware original Na. 2,195,453, mea April 2,1940', serlsl No. 234,099, October l0, 1988. Application for reissue February 17, 1942, Serial No. 431,229

(Cl. LIS-23) `11Clalms.

This invention relates to electric furnaces of the class adapted for carrying out chemical, metallurgical or heat-treatment operations, at suit` able high temperatures according to the treatment in hand. Particularly the invention pertains to an electricfurnace with tubular type of generated between the coarser particles of nlav I. terial, into which the electrodes project. Said material surrounds the chamber, in

which the treatment is to be carried out. in such a preferred arrangement that the sizeof the granules or particles decreases, from the inside or reaction chamber, which thus is continuously operable, the ores or other mixtures or. substances progressing longitudinally from furnace inlet to discharge through the chamber, e. g., with dow'nward trend to cooperate with gravity. The general objects are to aiIord increased rate of .output, with improved efficiency and thoroughness-I of reaction. and with reliable-maintenance and contf^l of treatment temperature and duration; and further advantages will appear from the following disclosure oi' an illustrative embodiment of the invention, including durability of apparatus, continuous relief of generated gases andv economy as to heat losses and current consumption.

In a furnace according to thepresent invention, the reaction chamber is refractory walled, its wall being closed against air entrance to the chamber, but of hollow structure or double-k walled to .provide gas interspaces constituting a longitudinally extending wall ilue, -from which nue leads an extension passage or conduit to a separate place of disposal or reception, as to a vapor condensing vessel; the inner wall part orr face being perforated for gas outflow from the chamberspace to the ue; there being a body of electrical-resistance-heating material arranged surrounding the outer wall part of the chamber wall and in heating relation thereto andY adapted to have suitable current supplied to it;

and co-operativeetherewith an interior mechanical feed device as a screw, of refractory material.

occupying the chamber and operable or relatively rotatable therein progressively to convey or cause the advancing feed of the mass of substances under treatment. By designating as refractory the chamber wall and the feed screw this term is intended in its broad sense of being resistant to the high temperatures of treatment, and preferably also to corrosion from the substances contacted; and these parts vshould. be heatconductive as well. The term gas is used in the broad sense of including vapors. As regards the resistance he'ating material this is preferably in subaccordance with the invention.'

'partzofsunilarmateliaL chamber wall towards the outside or casing, to an exceedingly fine condition; so that .the outer layer of the granular material is formed by 'a fine powder winch, by virtue of the very high internal resistance between its particles, actually functions as an insulator, both electrically and thermally; the granules of the inner layer of saidmaterial, however, having a relatively large size.

for example of about 3 to 8 mm., so that. electric arcs can be formed between the same.

In order that the above statements lmay more readily understood, reference is had to the annexed drawing, in which the single llreillustrates, in a vertical sectional elevation, one embodiment of an electric furnace constructedin The furnacechamber C has it interior space enclosed by its refractory wall I-I which is hollow and shown composed of aflrst wall part or inner cylinder l of graphite, petroleum coke, sillcon "carbide, zirconium carbide or other conductive material suitable for the purpose; and sux-4 rounding the inner cylinder, with a narrow interspace or ilue F between, an'outer cylinder or wall The furnacechamber C has its inner flue F. Interiorly the chamber is tted with a mechanical feed device or impeller screw lof refractory materlalsuch as graphite or petroleum divided or granular form. andthe generation of heat is effected in one or both of two ways, namely,.partly by the resistance encountered byY the electric current in itspassage throughthe furnwe or material, partly by small electric arcs coke. 'I'his driven feed device or screw. rotatable relatively to the chamber, occupies axially the chamber space so as to Aact directly on the solid substances under treatment and progressively convey or cause the advancing feed of the mass; and the pitch of said screw is shown as varying,

namely, increasing from the infeed or .upper end to the discharge or lower end of the furnace.' The screwfeeder extends upwardly and into a hopper l which serves for/supplying the material to be treated, 'fox-.instance suitably ground ore 'in mixture with any required agents. as iluxes.

' At one end, in this case the upper endpthe in terspace-F between the chamber wall parts or cyiinders l and 2 communicates, through a conduit or extension passage l, with a separate place of disposal as Aa condensing vessel "or chamber vl.

wall part I provided with upwardly inclined pel'iorations or narrow passages 3,'constituting exits for the es -cape of gases such as metal vapors to the wall Near the other end or the wan nue F is shown an inlet pipe vor passage 6 extending between an exterior point and the wall flue.

The furnace and chamber are shown with downfeed, being arranged upright, and the lower end of the chamber tube is shown as being enlarged and discharging at some distance vertically above and on to a conical distributor or screen 8, which serves for distributing the material discharged from said chamber over a discharge table 9, and each of theseparts 8 and il may be secured to the spindle or drive shaft ID y'of the impeller screw 4, and thus partake of th reduction that the speed of the shaft I and feeder 4 is, for exa iple, of the order of about one revolution per minute, but naturally varied according to the vdesired duration of treatment in any particular case.

Referring further to the feeding device or rotary screw 4, this is shown in its preferred form comprising a refractory and heat conductive stem or core l mounted on the operating shaft I D,

and feed ribs or screw threads 4b projecting from the core substantially to the chamber inner wall part i. By this arrangement the ground mass does not i111 the chamber but occupies only the annular space or path A between the core IlE11 `and the wall i. By having the screw stem relatively thick and the annular path relatively thin, as

shown, the advancing mass between these hot parts, which itself may be a poor heat conductor, becomes rapidly, thoroughly anduniformly heated throughout the mass, to the great betterment of the reaction or treatment.

The outer wall part 2 of the chamber wall is shown surrounded by a body Zik-2! of electricalresistance-heating material contained in a relatively wide space between the chamber and a refractory casing or jacket i6 of composition comprising asbestos, magnesia, aluminum oxide -or the like, said exterior casing shown restingon a refractory base or slab i1, which itself is supported by a steel framework, upon which also the bearings of the driving gearing are mounted.

Electric current is introduced to the mass Z-ZI by electrodes IB, of which three are shown as extended/through apertures provided, at different levels, in the jacket I6. Said electrodes sistance material, preferably granular and in The innermost layer 2li;`

graded arrangement. i. e., the layer adlacentto the chamber outer wall part 2, consists of relatively coarse granules,`

as of coke,- graphite, or the like. .The outermost layer 2|, i. e., the layer adjacent to the casing or jacket I6, consists of very fine or pulverized material such as soot (lamp black, carbon black) affording an insulating function, and optionally it may be mixed with magnesio.. aluminum oxide or the instance. briquetted. 'The space intermediate said layersl and 2| is lled with a layer IU of granu -lar carbon or the like, the size of these granules decreasing, in outward direction, for example, from a size substantially corresponding to that of the granules of the inner layer 20, substantially to a size corresponding to that of the particles 0f the outer layer 2|. The inner portion of the body 2,-20'-12l of heating material, when subjected to a suitable current, generates and maintains the desired temperature in the tubular wall of chamber C, lwhich is communicated to the advancing annulus of ore or other mixture and to the cylindrical core of the feed device operating in the chamber. j

The modus operandi of the described furnace is preferably as follows:

First, the electrodes IB are shifted or slid inward, until their inner extremities or wear tips directly contact with the chamber outer wall part 2, whereupon the current is switched on. The current will thereupon flow between electrodes principally through the chamber wall, which is thus quickly heated to the required ten'lnerature.

ment onward the electrical energy supplied through the electrodes I8 serves only for maintaining such temperature, the electrodes are readjusted and retracted a little from the chamber, whereby the current will thereafter pass for the greater part through the coarse carbon granules 20, which by that timehave already assumed a high temperature. As a consequence, smallelec tric arcs will be formed between said granules. generating heat thus and by resistance, and the total strength of the needed current will be consider'ably reduced. `The extent of retraction of the electrodes and therefore their degree of immersion in the resistance mass may be varied at will by wayof control'of the electric flow and genlike, and this layer may be suitably compressed. for 7'5- eration of temperature.

As stated, the very fine carbon powder or soot in the outermost layer in the space between the chamber wall and jacket li acts as a heat insulator, so that the jacket or casing remains relatively cool, minimizing heat loss.v Besides, said Y fine material also acts as an electric insulator,

especially when magnesio. or the admixed therewith.

If desired, the electrodes can be adjusted in position by automatic means, as under the control of a suitable thermostat, by way of controlling the heating action to maintain a desired temperature. y

Theseparate vessel or receiving chamber 'i can be used for collecting and condensing gaseous products that may be formed in the reaction chamber, for instance, vapors of metals, as aine. I The increasing pitch of screw 4 in downward direction towards discharge may in some cases be useful to prevent the solids underi1treatment from clogging thereaction chamber.

What is'claimedis:

1. An electric furnace comprising a base, areaction chamber with a hollow wall structure surlike has been vrounding said chamber, saidstructure consisting `sagre of inner and outer wall parts..with inclined chantreating solid substances or mixtures, having a nels in the inner vwall part of said hollow wall connecting `the reaction Achamber interior with the interspace or flue in thehollow wall, a condenser connected to said chamberA wall interspacean outer casing encircling said chamber wall structure with a space between said chamber wall and casing, means for introducing supplies of solid substances into vsaid chamber -f or treatment, means for discharging the treated substances from the chamber, an insulating layer located adiacent to the inner face of said outer casing and occupying the outer portion of said space, a plurality of concentric layers of resistance heating material constituting a heating zone between said insulating layer and the outer face of said chamber wall structure, said concentricv layers or zone forming the main furnace heating means and consisting of current conducting particles of which the size gradually increases in the direction from said insulating layer towards said chamber wall structure, and displaceable electrodes supported by said-outer casing and protruding through said heat insulating layer into said heating zone.

2. An electric furnace comprising a base, a reaction chamber with a hollow wall structure surrounding said chamber, said structure consisting of inner and outer wall parts, with inclined channels in the inner wall part of said hollow wall connecting the reaction chamber interior with the interspace or iluein the hollow wall, a condenser connected to said chamber wall interspace, an outer casing encircling said chamber wallvstructure with a space 'between said chamber wall and casing, means for introducing supplies of solid substances into said chamber for treatment. a screw conveyor within the chamber for feeding the substances through the same, the pitch of said conveyor increasing from its upper toits lower end, and means for. discharging the treated substances from the chamber, an insulating layer-located adiacent to the inner surface of said outer casing and occupying the outer portion of said space, a plurality of concentric layers of resistance heating material constituting a heating zone between said insulating layer and the outer face of said chamber wall structure,

. said concentric layers or zone forming the main furnace support or base and an outer enclosure or casing, and substance infeeding and discharging means, and comprising in combination therewith. a refractory-walled tubular reaction cham- -berarranged longitudinally between the furnace infeed and point of dischargeof the substances to be treated', said chamber wall being closed but of hollow structure to provide gas or vapor interspaces constituting a longitudinal wall ilue, with an extension passage leading from such ue to a separate place of disposal as to a condensing vessel, and said chamber wall having perforations in its inner face for outflow of gases or vapors fromthe .chamber interior to the wall nue, a

body of electrical-resistance-heating material arranged surrounding the chamber wall in heating relation thereto,. and provided with current-supplying Aor electrode members, and an interior mechanical feed device asA a rotatable screw of refractory material occupying and relatively operable within the chamber adapted progressively to convey or cause the 'advancing feed of the mass of substances under treatment. r

5. A continuously-operable high-temperature.

metallurgical electric furnace for treating ore -l lchamber wall having perforations in its inner face 'adapted for outdowof vapors from the chamber interior` to the wall iiue.V a bodyof electrical-resistance-heating material arranged surrounding the chamber Wallin heating 'relation thereto adapted to generate temperatures sumcient to vapcrize metals from such ore substances.

and provided with current-supplying or electrode members. and an interior mechanical feed device as a rotatable screw of refractory material occupying and relatively operablewithin the chamber adapted progressively to convey or cause the adv vancing feed therethrough of the mass of substances under treatment.

6.l Avcontinuously-operable electric furnace for treating solid substances ormixtures, having a furnace support or base and anouter enclosure or casing. and substance-infeeding and discharging means, and comprising in combinationtherewith, a refractory-walled tubular reaction chamber arranged between a higher furnace infeed means and a lower discharge means for the substances treated, said chamberv wall being closed feeding the substances to be treated to said I chamber from above and for discharging the same from below. an insulating layer located next tothe inner surface of said outer casing, a

plurality of concentric layers of current conducts ing Particlesdn a zone between said insulating layer, and said chamber wall-structure forming the heating means of the furnace, the particle size of said layers gradually increasing in the direction from said insulating layer inwardly but of -hollow structure `to vprovide gas interspaces constituting an upwardly extending wall flue, with an extension passage leading from the upper end of such flue to a separate place of disposal, and said chamber wall having perforations in its inner face for outflow of'gases or vapors 'from the cnamberlnterior to the wan nue. a bodyof electrical-resistance-heating material arranged towards said chamber wall structure, and displaceable electrodes supported by said outer casing.

4. A continuously-operable electric furnace for surrounding the chamber wall in heating relation thereto and' with electrodes to conduct current thereto, and an interior mechanical feed device comprising a rotatable screw of refractory materialoccupying and relatively operable within the chamber adapted progressively vto convey or cause the advancing downfeed ofthe mass of substances under treatment. at a predetermined rate oi' screw rotation and speed of downfeed.

7. An electric furnace as in claim 4 and wherein the body of electrlcal-resistance-heating niaterial is in subdivided or granular form coniined.

betweenthe chamber wall and the outer casing, such material being of graded sizes of particles methodically arranged with the coarser particles adjacent to the chamber and the ilner particles adjacentto the casing. i y

Y 8. An electric furnace as in claixn 4 and wherein the body 'of electrical-rasistance-heating material is in subdivided or granular form confined between the chamber wall and the outer casing', such material being of graded sims of particles methodically arranged with the coarser particles adjacent to the chamber and the finer particles adjacent to the casing; the layer which is near; est to the casing being composed of particles oi such fineness as afford insulation protecting thein the mechanical feed device or screw comprises a refractory central stem or core of substantial diameter thereby with the chamber wall defln. -ing an annular path for the advancing solids,

wherein rapid, thorough and uniform heating of the solids occurs.

11. An electric furnace as in claim 6 and wherein the feed screw pitch varies along its length with increase of pitch toward the furnace discharge.v

Damm. GARDNER. l 

